1. Field of the Invention
The present invention relates to binders for hydraulic compositions. The invention relates also to hydraulic compositions containing such binders.
2. Prior Art
Hydraulic compositions for extrusion molding often contain processing aids generally referred to as xe2x80x9cbinders.xe2x80x9dThe binders have until now been composed entirely of cellulose ethers, including alkyl celluloses such as methyl cellulose, hydroxyalkyl celluloses such as hydroxyethyl cellulose, and hydroxyalkyl alkyl celluloses such as hydroxyethyl ethyl cellulose. Given their excellent plasticity and water retention, the use of such cellulose ethers as a binder in hydraulic compositions makes the compositions readily amenable to extrusion even in the absence of asbestos.
However, cellulose ethers are expensive because they are prepared by the chemical treatment of refined natural pulp as the starting material. Efforts have been made to mitigate such costs by replacing some of the cellulose ether with other, relatively inexpensive substances, including such thickening agents as polyvinyl alcohol, starch and various chemically synthesized products (e.g., polyacrylamide, polyethylene glycol), or a highly water-absorbing resin. For example, JP No. 2884118 discloses a method comprising the use of a water-soluble cellulose ether in combination with an acrylic copolymer to give an admixture for extruding asbestos-free cements. JP No. 2812837 describes a method involving the use of a thickener composed of a water-soluble cellulose ether in combination with polyvinyl alcohol.
However, such thickeners have thickening properties and water-retaining properties which are inferior to those of cellulose ethers. As a result, the amount of binder components used in the composition increases and moisture distribution within the extrudate becomes non-uniform, which tends to lower extrudate strength and cause swelling after autoclave curing. Hence, the use of prior-art thickeners such as the above often lowers the quality of the extruded product.
It is therefore an object of the invention to provide a binder for hydraulic compositions which, when used as an extrusion aid in cement- or gypsum-based hydraulic compositions, allows the content of water-soluble cellulose ether to be reduced while maintaining the extrudability and water retention properties of the composition. Another object of the invention is to provide hydraulic compositions containing such a binder.
We have found that the use of a long-chain alkylbenzenesulfonic acid or a neutralization salt thereof in combination with a water-soluble cellulose ether as the binder in a hydraulic composition allows the amount of water-soluble cellulose ether included in the composition to be reduced while at the same time providing excellent extrudability and water retention.
Accordingly, the invention provides a binder for hydraulic compositions which comprises a water-soluble cellulose ether and a long-chain alkylbenzenesulfonic acid or a neutralization salt thereof. Preferably, the long-chain alkyl group on the long-chain alkylbenzenesulfonic acid has 6 to 18 carbon atoms. The water-soluble cellulose ether is typically an alkyl cellulose, a hydroxyalkyl cellulose or a hydroxyalkyl alkyl cellulose. The invention also provides a hydraulic composition containing the foregoing binder.
Preferred examples of the water-soluble cellulose ether used in the inventive binder for hydraulic compositions include alkyl celluloses, hydroxyalkyl celluloses and hydroxyalkyl alkyl celluloses. Specific examples include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose and hydroxyethyl ethyl cellulose. Preferably, the water-soluble cellulose ether has a viscosity, as measured for a 1 wt % aqueous solution at 20xc2x0 C., of about 100 to about 50,000 mPaxc2x7s. From the standpoint of cost, the use of a water-soluble cellulose ether having a relatively high viscosity is advantageous. A viscosity of at least 5,000 mPaxc2x7s is especially preferred.
The long-chain alkylbenzenesulfonic acid or a neutralization salt thereof forms a complex with the water-soluble cellulose ether, exhibiting a very strong thickening effect. It thus acts together with the cellulose ether to increase the extrudability and water-retaining ability of the hydraulic composition. This synergistic effect makes it possible to maintain the necessary extrusion performance even at a lower water-soluble cellulose ether content. Moreover, these binder components have surface active effects which improve compatibility, particularly with organic fibers and powder components such as cement, thus increasing dispersibility during mixing and, in turn, making it possible to reduce the content of water-soluble cellulose ether in the composition.
The long-chain alkyl group on the alkylbenzenesulfonic acid may be linear or branched, and preferably has from 6 to 18 carbon atoms. Specific examples of suitable long-chain alkylbenzenesulfonic acid compounds include dodecylbenzenesulfonic acid, octylbenzenesulfonic acid, hexylbenzenesulfonic acid, heptylbenzenesulfonic acid, nonylbenzenesulfonic acid, decylbenzenesulfonic acid, tetradecylbenzenesulfonic acid, hexadecylbenzenesulfonic acid, octadecylbenzenesulfonic acid, and also sodium salts thereof as well as salts prepared by neutralizing the respective acids with triethanolamine.
The number of carbon atoms is more preferably from 8 to 16, and most preferably from 10 to 14. The industrial production costs for long-chain alkylbenzenesulfonic acids and neutralization salts thereof in which the alkyl group has 19 or more carbon atoms rise to such a degree that even lowering the content of cellulose ether in the composition may provide little if any cost-reducing effect. On the other hand, because alkylbenzenesulfonic acids and neutralization salts thereof in which the alkyl group has 5 or fewer carbon atoms have only a weak complex-forming effect with water-soluble cellulose ethers, a reduced water-soluble cellulose ether content tends to result in poor extrudability.
The water-soluble cellulose ether and the long-chain alkylbenzenesulfonic acid or neutralization salt thereof are formulated in a weight ratio of preferably 30/70 to 95/5, more preferably 50/50 to 90/10, and most preferably 65/35 to 85/15.
The incorporation of too much long-chain alkylbenzenesulfonic acid or a neutralization salt thereof excessively lowers the content of water-soluble cellulose ether, greatly diminishing the water-retaining properties inherent to water-soluble cellulose ethers. As a result, when pressure is applied to the hydraulic composition inside an extruder, water separates out, making extrusion difficult to carry out. On the other hand, the inclusion of too little long-chain alkylbenzenesulfonic acid or neutralization salt thereof provides only a weak thickening effect in concert with the water-soluble cellulose ether and permits only a slight reduction to be made in the cellulose ether content of the composition. As a result, the objects of the invention may be difficult to achieve.
The amount of the water-soluble cellulose ether and the long-chain alkylbenzenesulfonic acid or a neutralization salt thereof included in the extrudable hydraulic composition is generally in a range of 0.1 to 5 parts by weight per 100 parts by weight of the combined amount of the subsequently described hydraulic substances (e.g., cement, gypsum) and aggregates (reinforcing fibers) other than the above-described water-soluble cellulose ether, long-chain alkylbenzenesulfonic acid or neutralization salt thereof, and water making up the composition. From reasons having to do with cost, an amount within a range of 0.2 to 2 parts by weight is especially preferred. Given that these binder components are used in particular as extrusion aids, they should be used in a degree that provides the water retention and plasticity required for extrusion. The inclusion of too little binder may fail to provide the necessary water retention properties or result in poor plasticity, making extrusion difficult to carry out. Conversely, too much binder increases costs and raises the tack of the composition, which can make the extrusion pressure unnecessarily high.
Cements that may be used in the hydraulic compositions in which the inventive binder is formulated include ordinary Portland cement, slag cement, early-strength cement, fly-ash cement and alumina cement. Gypsum-based hydraulic substances that may be used include primarily the dihydrate and hemihydrate forms of gypsum. The content of cement or gypsum-based hydraulic substances may be set as needed to achieve the required strength.
If necessary, an aggregate may be included in the hydraulic compositions of the invention. For example, primary use may be made of powdered silica. To produce a more lightweight material, use can also be made of expanded perlite, highly water-absorbing resins, styrene beads, inorganic hollow microspheres and organic hollow microspheres. When ordinary aggregate is used, the amount of aggregate in the hydraulic composition is preferably 0 to 90 parts by weight, and especially 10 to 90 parts by weight, per 100 parts by weight of the combined amount of hydraulic substances and aggregate. When lightweight aggregate is used, the amount of aggregate is preferably 0 to 60 parts by weight, and especially 10 to 50 parts by weight.
If necessary, additives for the cement or gypsum, such as retarders, accelerators, high-performance water-reducing agents and high-performance AE water-reducing agents may be used. The amount of retarder or accelerator included may be selected based on the condition of the hydraulic composition after extrusion and before curing, although use is generally made of 0.1 to 10 parts by weight per 100 parts by weight of the hydraulic substance and aggregate combined. Other additives, such as high-performance water-reducing agents and AE water-reducing agents, may be included in an amount sufficient to maintain the fluidity of the system, and generally within a range of 0.05 to 6 parts by weight per 100 parts by weight of the hydraulic substance and aggregate combined.
If the hydraulic composition is to be extruded, it is advantageous to add also reinforcing fibers. Examples of suitable reinforcing fibers include those used for the same purpose in the prior art, such as cristobalite mineral fibers, wollastonite, sepiolite and mica, and also other types of fibers such as pulp fibers, polyvinyl alcohol fibers, polypropylene fibers and aramid fibers. The amount of reinforcing fiber incorporated into the hydraulic composition may vary depending on the desired flexural strength and impact strength, although use is generally made of 0.1 to 30 parts by weight per 100 parts by weight of the amount of hydraulic substance (cement, gypsum) and aggregate combined. Use in an amount below this range may fail to provide a sufficient reinforcing effect, whereas the use of too much reinforcing fiber results in poor dispersion of the fibers, which may bring about instead a decline in strength. Water may be added to the hydraulic composition. A conventional amount of water may be used, the particular amount of water being selected according to the type of hydraulic composition.
In addition, macromolecules which are used together with conventional water-soluble cellulose ethers may also be added. Illustrative examples include synthetic water-soluble polymers such as polyvinyl alcohol, polyethylene glycol and polyacrylamide, natural water-soluble polymers such as guar gum, and polysaccharides that are the products of microbial fermentation such as Welan gum.